The present invention relates generally to indicating devices for electrical systems, and more particularly to a fault indicator device and electrostatically-actuated indicator assembly for use therein.
Various types of fault indicators have been constructed for detecting faults in power distribution systems, including clamp-on type fault indicators, which clamp directly over cables in the system, and test-point type fault indicators, which are mounted over test points in the cables or associated connectors. Such fault indicators may be either of the manually reset type, wherein it is necessary that the indicator be physically reset following each fault, or of the automatically reset type, wherein a fault indication is reset upon restoration of line current. Examples of such fault indicators are found in products manufactured by E. O. Schweitzer Mfg. Co. of Mundelein, Ill., and in U.S. Pat. Nos. 3,676,740, 3,906,477, 4,063,171, 4,414,543, 4,438,403, 4,495,489, 4,686,518, 4,706,016 and 4,714,916 of the present inventor.
Detection of fault currents by self-resetting fault indicators is often most advantageously accomplished by means of a reed switch located within the indicator housing having contacts in close proximity to the conductor being monitored. Upon occurrence of an abnormally high fault-associated magnetic field around the conductor, the contacts close and actuate circuitry which positions to a fault-indicating position an indicator flag visible from the exterior of the indicator. Upon restoration of current in the conductor the circuit repositions the indicator flag to a reset or non-fault indicating position.
The present invention is directed to a fault indicator and electrostatically-actuated indicator assembly for use therein, which, by avoiding the use of magnetic windings and associated magnetic pole pieces as used in previous indicator assemblies, decrease the complexity and cost of manufacturing of the fault indicator. In particular, the indicator construction of the invention utilizes a rotatably mounted indicator flag formed of a light-weight foil material which is positioned in a reset indicating position by electrostatic attraction to adjacent foil electrode surfaces which are maintained at a high electrical potential relative to the indicator flag by a capacitor charged from the power line, and to a fault-indicating position by a permanent magnet which magnetically positions the indicator flag in the absence of the electrostatic attraction. In an alternate version, the indicator flag is maintained in the reset-indicating position by magnetic attraction, and in the fault-indicating position by electrostatic attraction.
Accordingly, it is a general object of the present invention to provide a new and improved fault indicator.
It is a more specific object of the present invention to provide a new and improved fault indicator having an electrostatically-actuated indicator flag for indicating the occurrence of a fault current.
It is a further object of the present invention to provide for use with a fault indicator or the like an electrostatically-actuated indicator assembly which is simple and inexpensive to manufacture.